title: Halogen bond tunability I: the effects of aromatic fluorine substitution on the strengths of halogen-bonding interactions involving chlorine, bromine, and iodine.
abstract: In the past several years, halogen bonds have been shown to be relevant in crystal engineering and biomedical applications. One of the reasons for the utility of these types of noncovalent interactions in the development of, for example, pharmaceutical ligands is that their strengths and geometric properties are very tunable. That is, substitution of atoms or chemical groups in the vicinity of a halogen can have a very strong effect on the strength of the halogen bond. In this study we investigate halogen-bonding interactions involving aromatically-bound halogens (Cl, Br, and I) and a carbonyl oxygen. The properties of these halogen bonds are modulated by substitution of aromatic hydrogens with fluorines, which are very electronegative. It is found that these types of substitutions have dramatic effects on the strengths of the halogen bonds, leading to interactions that can be up to 100% stronger. Very good correlations are obtained between the interaction energies and the magnitudes of the positive electrostatic potentials (σ-holes) on the halogens. Interestingly, it is seen that the substitution of fluorines in systems containing smaller halogens results in electrostatic potentials resembling those of systems with larger halogens, with correspondingly stronger interaction energies. It is also shown that aromatic fluorine substitutions affect the optimal geometries of the halogen-bonded complexes, often as the result of secondary interactions.
authors.affiliation: Department of Chemistry, University of Puerto Rico, Rio Piedras Campus, San Juan, Puerto Rico 00931, USA. kev.e.riley@gmail.com
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Riley
authors.forename: Jane S
authors.initials: JS
authors.lastname: Murray
authors.forename: Jindřich
authors.initials: J
authors.lastname: Fanfrlík
authors.forename: Jan
authors.initials: J
authors.lastname: Rezáč
authors.forename: Ricardo J
authors.initials: RJ
authors.lastname: Solá
authors.forename: Monica C
authors.initials: MC
authors.lastname: Concha
authors.forename: Felix M
authors.initials: FM
authors.lastname: Ramos
authors.forename: Peter
authors.initials: P
authors.lastname: Politzer
mesh_terms: D001688:Biological Products / Q000737:chemistry*; D001966:Bromine / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D003460:Crystallization; D004581:Electronics; D004583:Electrons; D005461:Fluorine / Q000737:chemistry*; D006860:Hydrogen Bonding; D007455:Iodine / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D011789:Quantum Theory; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D001688:Biological Products; D008024:Ligands; D005461:Fluorine; D002713:Chlorine; D007455:Iodine; D001966:Bromine